1. Field of the Invention
The present invention relates generally to a lithium secondary battery formed by placing at least a positive electrode, a negative electrode, and a non-aqueous electrolyte in a battery case wherein a positive electrode connecting member to which the positive electrode is connected and a negative electrode connecting member to which the negative electrode is connected are electrically separated, and a lithium secondary battery provided with a positive electrode in which a positive electrode material is adhered to a current collector, a negative electrode, and a non-aqueous electrolyte.
2. Description of the Related Art
As a secondary battery having high power and high energy density, lithium secondary batteries featuring high electromotive force derived from oxidation/reduction of lithium in the non-aqueous electrolyte have come into wide use.
Examples of such lithium secondary batteries include a coin-type lithium secondary battery wherein a separator 3 impregnated with non-aqueous electrolyte solution is sandwiched between a positive electrode 1 in which a positive electrode material is adhered to a positive electrode current collector 1a and a negative electrode 2 in which a negative electrode material is adhered to a negative electrode current collector 12, and placed in a battery case 10. The positive electrode 1 is connected to a positive electrode connecting member 11 in the battery case 10 via the positive electrode current collector 1a whereas the negative electrode 2 is connected to a negative electrode connecting member 12 via the negative electrode current collector 2a. An insulation packing 13 composed of polypropylene or the like is provided around the positive electrode connecting member 11 and the negative electrode connecting member 12, the positive electrode connecting member 11 is bent to seal the space between the positive electrode connecting member 11 and the negative electrode connecting member 12 as shown in FIG. 1.
In such lithium secondary battery, stainless steel or aluminum has been generally used as the positive electrode connecting member 11 in the battery case 10, and stainless steel has been generally used as the negative electrode connecting member 12 because aluminum gets alloyed with lithium when aluminum is used.
In the above-mentioned lithium secondary battery, when the positive electrode connecting member 11 is composed of aluminum, there have remained problems that the positive electrode connecting member 11 can not be fully bent to seal the space between the positive electrode connecting member 11 and the negative electrode connecting member 12, thus moisture comes into the battery can 10 from the sealed portion, hence storage characteristics is degraded.
On the other hand, when the positive electrode connecting member 11 is composed of stainless steel, there have remained problems that the stainless steel used as the positive electrode connecting member 11 corrodes away by the non-aqueous electrolyte solution. Especially, when cobalt-lithium oxide, nickel-lithium oxide, or manganese-lithium oxide having a spinel structure is used as the positive electrode material to obtain a lithium secondary battery having high voltage, the stainless steel used as the positive electrode connecting member 11 corrodes away more intensively, thus the storage characteristics of the lithium secondary battery is remarkably degraded.
In the ordinary lithium secondary batteries, aluminum foil, foamed aluminum, and the like have been used as the positive electrode current collector 1a of the positive electrode 1.
However, when charge/discharge is carried out repeatedly to the lithium secondary battery using the positive electrode 1 in which the positive electrode material is adhered to the positive electrode current collector 1a consisting of aluminum foil or foamed aluminum, there have remained problems that the positive electrode material separates from the positive electrode current collector 1a, contact between the positive electrode material and the positive electrode current collector 1a is degraded, thus discharge capacity is gradually decreased, and hence sufficient charge/discharge cycle performance is not attained.
An object of the present invention is to bend a positive electrode connecting member in order to seal easily and properly a space between the positive electrode connecting member and a negative electrode connecting member in a lithium secondary battery formed by placing at least a positive electrode, a negative electrode, and a non-aqueous electrolyte in a battery case wherein the positive electrode connecting member to which the positive electrode is connected and the negative electrode connecting member to which the negative electrode is connected are electrically separated. Additional object is, in such lithium secondary battery, to prevent the positive electrode connecting member from corroding away by non-aqueous electrolyte solution, thus to improve storage characteristics of the lithium secondary battery even in a case in which cobalt-lithium oxide, nickel-lithium oxide, or manganese-lithium oxide having a spinel structure is used as a positive electrode material to obtain the lithium secondary battery having high voltage.
Another object of the present invention is, in the lithium secondary battery provided with the positive electrode in which the positive electrode material is adhered to the positive electrode current collector, the negative electrode, and the non-aqueous electrolyte, to prevent the positive electrode material from exfoliating from the positive electrode current collector when charge/discharge is carried out repeatedly so that the positive electrode material and the positive electrode current collector contact stably, thus to prevent discharge capacity from gradually decreasing for charge/discharge, hence to improve charge/discharge cycle performance of the lithium secondary battery.
A first lithium secondary battery of the present invention is formed by placing at least a positive electrode, a negative electrode, and a non-aqueous electrolyte in a battery case in which the positive electrode connecting member to which the positive electrode is connected and the negative electrode connecting member to which the negative electrode is connected are electrically separated, wherein said positive electrode connecting member is composed of clad material comprising one of aluminum or aluminum alloy and one of austenitic stainless steel or ferrite stainless steel, and the aluminum or aluminum alloy in the clad material is set in the positive electrode side.
As the above-mentioned first lithium secondary battery, when the clad material comprising one of aluminum or aluminum alloy and one of austenitic stainless steel or ferrite stainless steel is used as the positive electrode connecting member, strength of the clad material is higher compared with the case where only aluminum is used, thus the positive electrode connecting member is properly bent in order to seal fully the space between the positive electrode connecting member and the negative electrode connecting member. As a result, moisture is prevented from coming into the battery can from a sealed portion, hence storage characteristics of the lithium secondary battery is improved.
As the above-mentioned first lithium secondary battery, when the aluminum or aluminum alloy in the positive electrode connecting member which is composed of the clad material is set in the positive electrode side, the positive electrode connecting member is prevented from corroding away by the non-aqueous electrolyte solution even in a case in which cobalt-lithium oxide, nickel-lithium oxide, or manganese-lithium oxide having the spinel structure is used for the positive electrode of the lithium secondary battery to obtain the lithium secondary battery having high voltage. In the clad material, a resistant alloy is formed in the interface between one of aluminum or aluminum alloy and one of austenitic stainless steel or ferrite stainless steel, thus even in the case where aluminum or aluminum alloy in the positive electrode side is damaged for the contact with the positive electrode current collector, the austenitic stainless steel or the ferrite stainless steel is prevented from corroding away by the non-aqueous electrolyte solution owing to the resistant alloy, hence storage characteristics of the lithium secondary battery is improved.
When aluminum-manganese alloy is used as the aluminum alloy in the clad material, the alloy having superior resistance is formed in the interface between the aluminum manganese alloy and one of austenitic stainless steel or ferrite stainless steel, thus the austenitic stainless steel or the ferrite stainless steel is further prevented from corroding away by the non-aqueous electrolyte solution, hence the storage characteristics of the lithium secondary battery is further improved.
Examples of the austenitic stainless steel in the clad material include SUS316L, SUS316, SUS304L, SUS304, SUS201, SUS310S, SUS321, SUS347, and SUSXM7, and at least one of SUS316L, SUS316, SUS304L, SUS304 is preferably used. Examples of the ferrite stainless steel include SUS430, SUS430F, and SUS434, and at least one of SUS430 and SUS434 is preferably used.
The first lithium secondary battery is characterized in that the clad material comprising one of aluminum or aluminum alloy and one of austenitic stainless steel or ferrite stainless steel is used as the positive electrode connecting member to which the positive electrode is connected, and that the aluminum or aluminum alloy in the clad material is set in the positive electrode side. The positive electrode, the negative electrode, and the non-aqueous electrolyte used in the lithium secondary battery are not especially limited, but well-known material which have been generally used can be used.
A second lithium secondary battery of the present invention is provided with a positive electrode in which a positive electrode material is adhered to a positive electrode current collector, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode current collector consists of aluminum alloy which is containing 0.1 to 10 wt % of manganese and has a space member.
In the second lithium secondary battery, the aluminum alloy containing 0.1 to 10 wt % of manganese is used as the positive electrode current collector for the following reasons. When the amount of the manganese contained in the aluminum alloy is not more than 0.1 wt %, strength of the positive electrode current collector becomes weak, and the ability of the positive electrode current collector to hold the positive electrode material becomes weak, thus the contact of the positive electrode material to the positive electrode current collector is decreased when charge/discharge is carried out repeatedly, hence charge/discharge cycle performance is degraded. On the other hand, when the amount of the manganese contained in the aluminum alloy is not less than 10 wt %, the manganese in the aluminum alloy is likely to elute into the non-aqueous electrolyte, thus the resistance of the positive electrode current collector to the non-aqueous electrolyte is decreased, hence, the charge/discharge cycle performance is degraded.
As the above-mentioned second lithium secondary battery, when the positive electrode current collector consisting of the aluminum alloy containing 0.1 to 10 wt % of manganese and having the space member is used, the positive electrode material is held strongly in the positive electrode current collector, thus even in a case in which the charge/discharge is carried out repeatedly, the positive electrode material fully contacts with the positive electrode current collector, hence discharge capacity is prevented from decreasing, as a result, the charge/discharge cycle performance of the lithium secondary battery is improved.
In the second lithium secondary battery, as the positive electrode current collector having the space member, the positive electrode current collector having one type of structure selected from lath including wire lath or metal lath, and sintered member, foamed member, and aggregation of wire material which are having a filling space can be used. Especially, when metal lath is used as the positive electrode current collector, conductivity of the positive electrode current collector is improved, and the positive electrode material is held strongly in the positive electrode current collector.
As the aluminum alloy constituting the positive electrode current collector, an aluminum alloy containing 0.1 to 10 wt % of manganese and at least one element selected from copper, magnesium, and zinc is preferably used. When such aluminum alloy is used, the strength of the positive electrode current collector is further improved, thus the positive electrode material is held more strongly in the positive electrode current collector, hence, the charge/discharge cycle performance of the lithium secondary battery is further improved.
In adding at least one element selected from copper, magnesium, and zinc into the aluminum alloy, when the amount is too small, these elements do not effect sufficiently. On the other hand, when the amount is too large, the resistance of the aluminum alloy toward the non-aqueous electrolyte is decreased. Therefore, the amount of at least one element selected from copper, magnesium, and zinc to be added to the aluminum alloy is preferably set in the range of 0.1 to 2 wt %, and more preferably, 0.1 to 1 wt %.
The second lithium secondary battery is characterized in that the positive electrode current collector constituted of the above-mentioned aluminum alloy and having the space member is used. The positive electrode material, the negative electrode material, and the non-aqueous electrolyte used in the lithium secondary battery are not especially limited, but well-known material which have been generally used can be used.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiment of the invention.